This invention relates to precision pumping, precision ratioing and mixing, precision vacuum degassing of work liquids and precision dispensing; both apparatus and method, certain of which have utility alone or in various combinations. The new precision pump/dispensing and precision mixing mechanisms are particularly useful in and shown in the environment of a new method and apparatus for vacuum dispensing and degassing of work liquids but are also very useful in other methods of dispensing of single or multi-component work fluids.
Thus, while the instant invention will be discussed in the art of vacuum dispensing which it advances, it will be appreciated that controlled repeatable programmable precision pumping for non-vacuum dispensing, and the controlled programmable precision mixing/ratioing of work liquids for non-vacuum dispensing, each have many applications outside of the vacuum degassed work fluid dispensing field.
High precision electrical and electronic products may require void free encapsulation of electrical/electronic components so that electrical/electronic characteristics are repeatable within very very close tolerances during production runs on a plurality of work parts. Minute cavities in encapsulation materials filled with gas (in materials such as epoxys, silicones, urethanes, etc.) can cause change of the electrical characteristics of the encapsulation material on the workpiece. Where ultra high precision is required, many of these two party materials are both degassed by vacuum techniques prior to dispensing and then dispensed under a vacuum so as to completely or almost completely degas such materials. Further the degree of precision of electrical characteristics in certain depositions also require exquisite precision control of pumping, ratioing, mixing and viscosity of the deposited work materials since the physical/chemical properties, the volume and exactness in location of the deposited work liquid materials all are capable of affecting the electrical characteristics and are therefore affected by such control.
In the apparatus and system under discussion, there is featured two part material dispensing under vacuum, wherein the work fluid materials are degassed prior to and after dispensing. Also adjustable programmable shot size of the mixed materials for precision volume dispensing is featured, with simultaneous precise ratioing of the work fluid and work part indexing control. Further the entire apparatus and system features adjustable programmable operations for single time or automatic repeatable operations. The complete control of the material flow (temperature, vacuum, pressure, etc.), the pumping (frequency and amount), and the ratioing, mixing, dispensing operations are controlled by a software program which may be used on widely available and well understood personal computers.
In broad brush, a void free production method and apparatus are provided having the work liquids (resin and catalyst) loaded into separate pressurized containers and conveyed to separate vacuum tanks where a whirling disc slings and atomizes the individual work materials unto the walls of their respective tanks. The material then forms a thin film on the sides of the tanks which is degassed by the maintenance of a vacuum in the tank while the work liquid film travels to the bottom of its tank.
The work material(s) is continually agitated in the tank(s) to maintain consistency and keep any fillers in the material(s) in suspension. The material(s) is the positively removed from the tank(s) through an auguring mechanism(s) (in this novel method and system) to then enter the pumping mixing system where the two parts of the work material(s) are brought together and statically or dynamically mixed.
Heretofore in the prior art, materials in a vacuum system were dispensed in a manner whereby a positive pressure was not kept on the work materials downstream of the vacuum tanks. For example, in the mechanism shown in A. L. Kraft U.S. Pat. No. 3,521,789, the degassed liquid leaves the vacuum tank(s) through the action of the metering piston which coacts with the cylinder. However, this apparatus does not keep a positive pressure upon the work materials in the system downstream of the piston throughout the relative movement of piston and cylinder and it appears that negative pressures are possible at transitory times in the normal operation. Thus, over time, in Kraft, a breakdown of seals or joints anywhere in the system downstream of the pump/cylinder will cause a reentrainment of gaseous contaminant into the work material through such failed seals or joints in the system intermediate the pump/cylinder and the dispensing outlet.
In the instant invention, by keeping of a positive pressure on the work materials throughout the system after exit of the vacuum tank(s), the entrainment of gas, when minute failures of seals and joints occur, is prevented so that void free dispensing is not jeopardized.
Additionally, there is located, intermediate the vacuum tanks and the delivery dispensing head(s), an extremely high precision positive displacement pump(s) for high precision control of the delivery of the fluid materials to the mixing head. The degree of precision provided is so different in degree, that it differs in kind from those heretofore used in the art. The control, in broad terms, is accomplished by a computer, a software program, computer peripherals and stepper or servo motors driving a positive displacement flushing action pump/cylinder.
Control of volume of amount of work liquids dispensed is also essential in many sophisticated areas including electronic applications. Primary control is achieved by control of the relative movement of a positive displacement piston and cylinder. Adjustable control allows versatility of work piece throughout. Timing (actuation) control of the pump mechanism affords integration with other automatic techniques and apparatus such as workpiece indexers and movers. It is self-evident that accuracy, both in time and volume, is critical to quality, as measured by precision of both volume dispensed and the location area on the work piece (position) of the dispensed material. Exacting dispensing control is disclosed herein and is provided by the generation of an electrical pulse stream which, through either stepper or servo motors, may be used to actuate the relatively moving element(s) of the pump piston and cylinder. A linear motor or a ball screw mechanism or other drive mechanism such as cable/drum, rack and pinion, or cams may be interposed between the motor output and the piston or cylinder. Alternatively, the motor output may be connected directly to the piston or cylinder. Software and computer peripherals provide generation and control of the pulse stream, both frequency and duration, such that with a computer, control may be provided in programmable fashion. The control is so refined that movements of the pistons(s) relative to cylinder(s) may be easily obtained in the range of 100,000 to 10,000,000 of one inch, (0.00001 to 0.0000001) inches over a substantial range of more than one inch of stroke movement. By simultaneously providing pulse streams to multiple pump/cylinders, control of the multipart work liquids for accurate ratioing therebetween is provided.
Proper viscosity and material uniformity of the work liquids on a consistent basis is necessary for precision dispensing. This can be aided by temperature sensing and control mechanisms for the work liquid materials. To insure precision, temperature sensing and feedback control is provided at the tank and at various other points in the dispensing system, all coordinated through the computer with proper software and hardware.
The workparts which are to be filled or encapsulated (poured) or have dispensing thereon may be disposed in a vacuum dispensing chamber where the actual dispensing will take place. This vacuum dispensing chamber causes further evacuation of any residual gases in the dispensed work material or in the work piece interstices and (at least in batch systems) is preferably organized and operated as a multi-outlet and multi-station apparatus. To this end the material to be dispensed may be routed through a manifold for simultaneous multipart dispensing. For high precision the individual outlets from the manifold my be further controlled by very high precision pinch valves which adjust for different lengths, or routes of travel of, the mixed work liquid after leaving the mixer. Each of the pinch valves have micrometer adjustments for material flow rate adjustments to compensate for distance from the central source input manifold. By this manner, simultaneous high precision multiple dispensing heads may be used while providing part to part precision. Also the pinch valves, when coordinated with the precision pumps, prevents ooze or drip and suck back may be provided. Alternatively, individual output pumps for each dispensing head may be used, their volume adjusted either mechanically or by computer controlled pulse stream.
Thus in general the invention features as the broad object, high precision liquid material dispensing of work liquids.
Further the invention has as an object to provide high precision positive displacement pumping of work liquids which may be pre-selectively adjustably controlled.
A further object is to have a void free work liquid dispensing method and apparatus for production of parts.
Another object of the invention is to have versatile production capabilities in an apparatus and system where the dispensing production may be had under either vacuum circumstances or with open pour.
A further object of the invention is to have high production rate capabilities with multiple port dispensing.
A still further object of the invention is to have a method and apparatus with all operating control through easy programming and recalling of programs operable by relatively unskilled operators.
A further object of the invention is to provide high reliability, low maintenance, compact size and clean design readily adapted for association with other automatic systems.
A still further object of this invention is to provide a high precision versatile apparatus for positive displacement dispensing of a first work liquid, there being operator selective adjustable means for controlling the motion between a pump and a cylinder where the relative motion can be in any repeatable or variable selected time conditioned dependent interval between movements such that a selected constant or variable relative velocity of movement may occur between the pump and the cylinder for high precision pumping in a controlled fashion.
Another object of this invention is to provide an apparatus where the relative movement between the pump and the cylinder may be controlled in repeatable adjustable fashion where the movements are less than 1/100,000 inches over a stroke of in excess of an inch.
A further object is to provide an apparatus and system where the movements between controllable steps are from a perceived practical standpoint, continuous in nature.
A still more specific object of the invention is to provide for relative movement of a cylinder and piston wherein a computer controlled pulse stream provides measured repeatable controlled movement therebetween in discrete increments.
Further and more specific object of the invention is to provide a system and method wherein a precision pump may be respectively used to control each individual work liquid and provide accurate adjustable programmable ratioing of at least two different work liquids in delivery thereof at a mixing head for later dispensing at a dispensing head.
A further object of the invention is to provide an apparatus and method for precision vacuum dispensing where the work material is removed from a degassing chamber so as to maintain a positive pressure on the work liquid above atmospheric pressure throughout the system until delivered at the dispensing head to prevent the later entrainment of unwanted gases through seals or joints after the desired degassing of the work liquid.